The invention relates to ophthalmic lenses. In particular, the invention provides lenses that are useful in the correction of presbyopia and astigmatism.
As an individual ages, the eye is less able to accommodate, or bend the natural lens, to focus on objects that are relatively near to the observer. This condition affects is medically known as presbyopia. Typically aging patients have varying combinations of presbyopia, astigmatism, myopia, and hypermetropia, and fitting these patients with contact lenses presents a challenge. In particular, correcting the vision of patients with astigmatism and presbyopia is difficult, and over the years a number of methods of dealing with this problem have been suggested.
One known method, is a contact lens that has a series of alternating spherical optical powers corresponding to the spherical distance power prescription, the spherical near power prescription, and a third spherical power which takes the cylindrical power into account, but does not use a cylindrical surface. Another approach to this problem combines a multifocal toric lens that corrects corneal or lenticular astigmatism with a correction for presbyopia. This contact lens has a front surface and an opposite back surface where one of these two surfaces has multifocus annular toric rings with alternating near distance and far distance powers, that corrects astigmatism.
Although these lenses improve the visual acuity of an astigmatic presbyope, they suffer from at least one drawback. Both contact lenses correct for astigmatism in the near vision as well as the far vision. When near power is added it adds more power to the distance power. By adding cylinder power to both distance and near power, the plus value of the near power is partially negated by an extra minus cylinder power. Therefore, a need exists for a contact lens which may be used by astigmatic presbyopes which corrects the astigmatism in their distance vision without unnecessarily correcting the astigmatism in their near vision. It is this need that the lenses of this invention meet.